Selective communication system



June 17, 1952 c. H. HOEPPNER SELECTIVE COMMUNICATION SYSTEM 3 Sheets-Sheet 1 INVENTOR. CON RA D H. HOEPPNER Filed March 18, 1946 ATTORNEY June 17, 1952 c. H HOEPPNER 2,600,405

SELECTIVE COMMUNICATION SYSTEM Filed March 18, 1946 3 Sheets-Sheet 2 INVENTOR. CON RAD H. HOEPPNER ATTORNEY June 17, 1952' c. H. HOEPPNER 2,600,405

- SELECTIVE COMMUNICATIONSYSTEM Filed March 18, 1946 s sneets-sfieets INVENTOR. CONRAD H. HOEPPNER ATTORNEY Patented June 17, 1952 UNITED STATES PATENT OFFICE SELECTIVE COMMUNICATION SYSTEM Conrad H. Hoeppner, Washington, D. C.

Application March 18, 1946, Serial No. 655,356

(Granted under the act of March 3. 1883. as amended April 30, 1928; 370 G. 757) 7 Claims.

to a particular frequency regardless of its source- In control signal communication for example, single frequency selectivity may require a discrete frequency for each control. For a multiplicity of controls, a wide section of the frequency spectrum may be required in order to secure the'necessary discrimination between signals. controls is subject to actuation by energy of its correspondin frequency regardless of the source of that energy, a condition which, particularly in radio control systems, leads to erratic control.

It is possible to avoid erratic operation to a large extent and to actuate a number of discrete controls greater than the number of frequencies employed by providing a plurality of frequency selective circuits at the receiver in such a manner that only energy which is of a plurality of frequencies will be accepted to actuate a given control. While such combination coding isadvantageous as compared with simple single frequency selectivity, it fails to achieve the same efficiency of utilization of frequencies as a coding system in which, for each control, there must not only be a plurality of frequencies, but the necessary frequencies must appear in a particular order in a particular time relationship. Such a system ofv coding may be called time permutation*codin'g'or simply permutation coding.

It is an objector" this invention to provide meth- 0d. and aparatus for permutation coding.

It. is another object of this invention to provide method and apparatus for signal discrimination on the basis of frequency composition.

It is another object of this invention to provide method and apparatus for accepting or rejecting. an input signal in accordance with its frequency occurrence characteristics.

It is another object of this'invention to provide .a circuit which responds to produce an output signal only to a particular plurality of signals applied in a particular order within apredetermined interval of time.

Any one of the- Otherobjects and features of this inventionwill become apparent upon a careful consideration: of the following detailed description when taken-v together with the accompanyin drawings in;

which:

.Fig. 1.is the circuit diagram of oneexemplary embodiment of this invention;

Fig.2 is the circuit diagram of a variant em.- bodiment of thisinvention; and,

Fig. 3 is the circuit diagram of another variant embodiment of this invention.

In a communication systeminwhich eachitem.

of intelligence is conveyed. by a plurality of: fre:-

quency components, mer combination.ofthosecomponents limits their common used. to :only one intelligence item. If, howeveigpermutationx be employed, the common use of a. plurality of frequencies may result in a number of discrete arrangementseach of which may correspond tOTa. different item of intelligence. For example, three:- different frequencies, which, in combination, yield? only one arrangement, in time permutation, yield six arrangements.

- Reference is now had to Fig; I, the'circuit. diagram of apparatus for time permutation coding:

constructed according to the teachings of this. in.- vention. A signal comprisingenergy of three-frequencies F1, F2, and F3 occurring in a predetermined time order must be applied at input terminals I in order to produce anoutput signal at output terminals 2. Inthis embodiment-the input signal isapplied to a frequency selective: input circuit comprising parallel inductive'branch 3 and capacitive branch 4. Inductive .Windingr? has acore 5 of magnetic material, such as silicon steel, or one of various available alloys of iron nickel and cobalt, or powdered iron. On this core 5' are two other windings Band 1. With this construction, the flux resulting from the flow of'current in windings 5 and l affects the flux density within core 5 with respect to winding 3. Since the flux density is changed, the permeability isthe incremental inductance of winding 3. When no current flows in winding 6 or winding 1, wind ing 3 contributes its highest value of inductance to the parallel circuit which it formswith capacitive element a. Under such a condition, the resonant frequency of the parallel circuit is at its lowest value. If current flows in either winding 6 or winding 1, the resonant frequency of the parallel circuit is increased by an amount which depends largely upon the number of turns in those windings and by the magnitude of the current. Thus the current through those Windin may be controlled to effect a change in the resonant frequency of the parallel circuit.

Tubes 8 and 9 represent the vacuum tube components of a self returning switching or multivibrator means for producing a time interval defining gating voltage which appears as a positive excursion at plate II! of tube 9 and as a negative excursion at plate I! of tube 9. In particular. tube 8 is a normally non-conducting tube held so by positive cathode bias. It will, however, conduct to produce a negative signal at its plate l2 when a signal applied at input terminal I comprises energy of a frequency which develops the resonant frequency response of the parallel circuit comprising inductive winding 3 and capacitance 4. Such a negative signal at plate I2 of tube 8 is communicated through capacitor I3 to grid I4 of tube 9.

The right hand element of tube 9 of which plate II] is a part is normally conducting since grid I4 is normally at the same potential as cathode l5. The normal (quiescent) flow of current through the right hand element of tube 9 holds the left hand element, of which plate II is a part, non-conducting by virtue of the bias generated across resistor I6; A negative signal at grid I4, such as that supplied by tube 8, reduces the cathode bias on the left hand element of tube 9 permitting it to conduct and reverse the conditions of conduction and non-conduction within tube 9 for a definite interval of time. This normal cathode coupled self-returning multivibrator action is, of course, accompanied by the appearance of a positive gating voltage at plate I (right hand element non-conducting) and of a negative gating voltage at plate II (left hand element conducting). The duration of these gating voltages is determined essentially by the interval of time required for capacitor I 3 to discharge sufficiently for the right hand element of tube 9 to resume conduction. This interval may be fixed within wide limits substantially by choice of capacitor I 3 and resistors l1 and I8 in its discharging circuit.

Tube I9 is connected in series with winding 6 on magnetic core and represents a means of controlling the current which flows through winding 6. To maintain a high Q in the resonant circuit 3, 4 it is preferably that tube I9 be of the pentode variety. Grid 20 of tube I9 is so connected to the voltage divider comprising resistors 2|, 22, and 23 between plate I9 of tube 9 and (C) potential that tube I9 may only conduct when the right hand element of tube 9 is non-conducting, i. e. during the generation of the gating voltage.

Tubes 24 and 25 are the vacuum tube components of a second multivibrator means for producing a time interval defining gating voltage similar in all respects to the means comprising tubes 8 and 9 except that tube 24 is a dual control tube requiring positive signals on both grid 26 and grid 2'! simultaneously before a negative keying signal is applied to tube 25 to institute the generation of the gating voltage. Grid 2'! receives the resonant circuit output of the parallel circuit comprising winding 3 and capacitance 4 while grid 26 holds tube 24 non-conducting ex- 4 cept during the interval defined by the positive gating voltage appearing at plate 19 of tube 9.

Thus it will be seen that no signal may reach tube 25 except during the existence of the gating voltage produced by tube 9 and that during that gating voltage the frequency required to develop the resonant frequency response of the parallel circuit and thus apply a keying signal to tube 25 through tube 24 is changed by the flow of current through winding 6.

Tube 28 is a current controlling means responsive to the gating voltage produced by tube 25 in much the same manner as tube I9 is responsive to the gating voltage produced by tube 9 and is also preferably of the pentode variety. In this particular embodiment, tube 28 is a normally conducting tube so that its action is to stop the flow of current in winding 1 and thus decrease the resonant frequency of the parallel circuit comprising winding 3 and capacitance 4 during the interval of time defined by tube 25 gating voltage. Thisaction is accomplished by connecting grid 29 of tube 29 to plate 30 of tube 25 rather than to plate 3i. A negative, rather than positive gating voltage is thus applied to tube 28 during the interval defined by the operation of the second multivibrator means.

Tube 32 is a dual control or coincidence tube so negatively biased at both grids 33 and 34 that positive signals must be applied simultaneously to both grids in order to cause it to conduct and produce a negative output signal at terminals 2. Grid 33 is arranged to receive the resonant frequency response of the parallel circuit of winding 3 and capacitance 4 while grid 34 is responsive to the positive gating voltage generated at plate 3i of tube 25. It will be seen that the resonant frequency response of the parallel circuit will cause tube 32 to conduct to produce an output signal only during the existence of the gating voltage produced by tube 25 and that, during the existence of that gating voltage, the signal frequency developing that resonant frequency respouse will be decreased by the stoppage of current flow through winding 7.

In operation and in the absence of an applied signal at input terminals i, the right hand elements of tubes 9 and 25, and tube 28 are con ducting while the remainder of the tubes are non-conducting. The resonant frequency F1 of the parallel circuit comprising winding 3 and capacitance 4 is thus fixed by the flow of current through winding I at a value different from resonant frequency F3 (that which is fixed by the circuit elements in the absence of current flow through either winding 6 or Winding 'i') From the earlier explanation of the action of the plural windings on magnetic core 5, frequency F1 is thus greater than Fa.

Let it be assumed that a signal of frequency F1 having maximum peak amplitude limited in value by suitable preceding limiter circuits is applied to terminals I. This signal develops the resonant frequency response of the parallel circuit, tube 8 produces its keying signal, and tube 9 proceeds to generate its gating voltage. During the interval defined by this gating voltage, tube I9 conducts to alter the resonant frequency of the parallel circuit to a value F2 (corresponding to current flow in both winding 6 and winding 1). Also during this interval, tube 24 is unbiased at grid 26 and is ready to receive a signal from the parallel circuit. Now let it be assumed that, during this interval, a signal of frequency F2 is applied to terminals I. This sigaccents nalidevelopsfitheresonant: frequency; response: of the parallellcircuitptube: 24 i-produceszitsi keying signal andrtube w proceedsitoi generateritsigating voltage? The circuiti elements associated with tube a' areso -chosen thatrthe gating? voltage generatedi byii tube "'92 is ofi-a; duration just? sufficient to al-lomtheisignalfof Erfrequency. to place tube 25 in'toperation; Thus;ithe Igatingyoltages produced by the two multivibraton'meansr'overlap' verylittle 1 in: time and durin'e'fthe interval defineitby' tube:z'ir gatingl voltage, tube I Skis; cut oifs ltsrquiescentistatey-"andi tube? la -is? also; cut off:- (by? the: gating: voltage of tubefi 25) During the tube 25: intervanrthe i parallelvcircuit; has: a resonant frequencyih d tube uaiszunbiasedat grid Streadytoneceive ssignalifrom theiparallel circuit on; grid 33: NOW' let'x'it be lassumedthat; during: 'thisJlast' interVaLJ a signal 1 of Trequency Eerie: applied: att'termina'ls I: I This: signal .develops :the'. resonant frequency response or the parallel cir'cuitf'andiitubes 32: is caused :to: conduct torproduce an outputvsi'gnal tati terminalsi 21 1 'In-isunnnaryof theeforegoing:operatiomaa sig *nal: comprising three: different' frequencies E1,

Fznandi'Eaghaving a tim'e occurrence in the-order named antimaving fa time relationship suchi-that frequencyaF "waszapplied att terminals 1 "during the: interval defined" by the first multivibrator means (tubes and; 9)" and :such th'at iiirequency Fax-was aappli'ed: at terminals I rdurim; thes-inter val; defined: by the second' ilmultivi'brator "means wasznecessary. in order 4 to produce ani: output signal at "terminal 2;": In i this embodiment F3 represented-the lowestfreq'uency (moi-current flow in .either-winding fi or winding:- 1) Fa-represented the fhighest frequencyr 1 (current-,2 flow "in both' winding ffi'fand winding 1 and F1 represented'f an: intermediatefrequency (current flow iilI-WViIIdingf'. 1': only) 'Ilfis*-arran gementf E1 F2, anuzira is? only one? of the: six possible perrmita tions :of these three Tfrequ'encies.

r To'fillustrate circuit arrangements' for 'a' di fier ent'code; fort-example where Fi is low,"F2 -inter= mediate andzFa high; it i is 'merelyinecessary to changeithec connection: of 'gri'd 2 9i 'so i that it goes' to'ranode 3 I instea'd'of 'anod 301 Thus the low frequency Friwill: reverse the? conductive' condL tions of l the":trigger '-'circuit' of itube i bringing tube l 9* to? conduction to draw-"'currentithroug'h winding 6. When thisihappens :tlrerrreduc'ed in ductance -renders vthe ciruit sensitivettmthe intermediatefrequency" F2 4 to falter: the 'condition o't the-trigger circuit 'oftube "2 5 ythe'reby bringing tubes :to conduction through". winding'i'll' With conduction 'thus iestablished' throughi both Wln'd' ings -6 and: l, the'circuit isadju'sted: to :theLhighestf-requency-and 'withtube -32 umblocked' at grid 34; (output -signals can be realized; It'is'atonce apparent for this-thatthe unstable: period :ofthe trigger circuit of=tube'--:9 -must persist :for: at least the duration of the F2 andFssignal periods; It-should be noted "that the circuit will not-be actuated if. the chosen signal. frequency-'combinae tion prim, F2 etc: occursimultaneously because the limited input signal will not contain individual componentsiof sufficient amplitude to operate the circuits associated-with tubes 9 and a resonant'circuit lo. Winding 4-I hasaemagnetic core 42 and undergoes changes-in its incremental vinductance aby virtue-of the-passage of current directly 'thrizaugheit rather than through discrete 6 magnetically linked windingssas in the caseof the": embodiment of Fig; 'Currentwcoritrolling tubes 43% and '4 4 are coimectefd= in parallel v with each *otherand in series with winding? 41 *When they 'ia-re causedto'conduct; theyi super 'aose" a D: 0. flux on the inductance tochan'ge the resonant frequency ofparallel-circuit Quin-accordance with the operation or the first multi vibrator: means (tubes 1 4'5 and 46 and 'the 'sec- 0nd" multivibrator'*means*=(tubes-'41 and 489 5 inputa signalcomprising energy? of three frequencies' occurring inapredetermined 'ordermust be applied at input terminals flainprder 'tb cause tube 50 to conduct and produce an outjut signal at'terminals 51:. Thesamepermutations are-'po'ssible'in this' embodiment as were possible incthe embodiment or: Fig. 1-. A radio frequency choke 52 in series with the current 'controllin tubes 43" and 44" and winding: 41 hasbeen found of value in preventing? premature r triggering of the subsequent:multivibrator means or coincidence tube 'by l the sudden starting of conduction b'y'the'wurrent controlling tubes and to" prevent l'oadingiof the resonant circuit 40' by tubes-13; 4'4;

' In 'Fig'; 3; to-which reference is now' hadtis shown a variant embodimentin- Wh'ich'the capacitance rather than the inductance ofthe input 'circuit is-cha'nged'by each succeedingire quency elementofaninput signal: -In-this'em-- bodiment, both tubes Wand 61 are normally non-conducting: Eachhas in its plate'circuita respectivedouble contact, normally open, slow release, relay 62'an'd'63; These relays'are-ene'r giz'ed' to close their contacts only when the particular tube with which they-'are--assoclated is causedstozcond'uct. Onceenergized bya :mom'entaryssigna'l, the--'r.elays arequire" an interval of time to dee-energize (i-e; slow releaser which extendsubeyon'd' the existence of:the momentary signal. In operation, an input-*sign'al "comprisingienergyaof three frequencies-"F11; F12; and-:F a ofdescending: value and in thatorder: may: be applied-to input-terminals 6'4. Frequency-F11; of the: value :required to develop the resonant ire-quencysresponse of the parallel circuit-Icemprising inductance" 65 and; capacitance 66; unbiases tube and thereby. energizes irelay- 62. Relay; 62'; in closing its contactsri adds -capacitame- 67 to capacitance: 66rto alter the resonant input" frequency: to: F12. Itvalsow connects grid fifl 'of'tube -61 to' the input circuit i so as-to -ready it 1 forthe: next frequency element of-' the: "incoming: signal- Thisa-element; frequency F12; :de-

velopsthe resonant frequencyresponse of the input-circuitand unbiases 'tube :61 --to' close-.-relay circuit some to readyit for Fix; the finalitrequency element of the incoming: signalfl F re-'- quency- F13 at. input terminals "64 develops-the resonant frequencyresponse of the input' circuit and this is communicated to:= output terminals 19' to' const-itutethe output signale It will be apparent :to those-versed in the art that a wi-de variety of changes may be -made :in: the foregoing circuits, none of which exceed the' teachings-pf I this invention. Such changes as providing" a plurality ofinput circuits each "of a particular frequency and eachirendered responsive inn-turn rather than a- -single 'circuit the -=resonantFirequencyof which is-altered as each signal' element is, received will. beseen to be aha-obvious variation "Since certain further changes may be made in the foregoing constructions and different embodiments of the invention may be made without departing from the scope thereof, it is intended that all matter shown in the accompanying drawings or set forth in the accompanying specifications shall be interpreted as illustrative and not in a limiting sense.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon ortherefor. i.

What is claimed is:

1. A permutation coding circuit comprising, a saturable core reactor, a capacitance connected with said saturable core reactor forming a parallel resonant circuit therewith, means for applying'incoming signals to said parallelcircuit, a

sequence of means each for changing, for an int'erval of time, the degree of saturation of said saturable core reactor in response to the resonant frequency output of said parallel circuit, each memberof said sequence except the first being responsive to said resonant frequency output only for the interval of time during'which the immediately preceding member of said sequence changes the'reactance as said, and a coincidence point connected to said parallel circuit and to the last member of said sequence for obtaining an output signal from the resonant frequency output signal of said parallel circuit only for the interval of time during whichsaid last member changes the degree of saturation of said saturable core reactor as said.

2; A permutation coding circuit comprising, a magnetic core inductive winding, a capacitance connected to form a parallel circuit with at least a portion of said winding, means for applying incoming signals to said parallel circuit, a sequence of serially connected means for .producing gating voltages each connected to said parallel'circuit and each, except the first, operatively responsive to the resonant frequency output of said parallel circuit only for the duration of the gating voltage produced by the immediately preceding member in said sequenceja plurality of direct current-controlling means each connected to a respective member of said sequence and operative responsively to the gating voltage of the member to which connected to alter the incremental inductance of said winding, and coincidence tube means connected to said parallel circuit and to the last member in said sequence operative responsively to the resonant frequency output of said parallel circuit to produce an output signal only for the duration of the gating voltage produced by said last member.

3. A permutation'coding circuit comprising, a

magnetic core inductance, a capacitance conthe first operatively responsive to the resonant frequency output of said parallel circuit only for the duration of the gating voltage produced by the immediately preceding multivibrator means in said sequence, a source of current, a plurality of direct current controlling means each connected in series with said source of current and at least a portion of said inductance and to a respective one of said multivibrator means and each operatively responsive to the gating voltage of the multivibrator means to which connected, and coincidence tube means connected to said parallel circuit and to the last multivibrator means in said sequence operative responsively to the resonant frequency output of said parallel circuit to produce an output signal only for the duration of the gating voltage produced by said last multivibrator means.

4. A permutation coding circuit comprising, a magnetic core inductance having a plurality of discrete magnetically linked windings, a capacitance connected to form a parallel circuit with one of said windings, means for applying incoming 'signalsto said parallel circuit, a sequence of serially. connected multivibrator mea'ns for producing gating voltages each connected to said parallel circuit and each, except the first, operatively'responsive to the resonant frequency output of said parallel circuit only for the duration of the gating voltage produced by the immediatelypreceding multivibrator means in said sequence, a source of current, a plurality of direct current controlling means each connected in series with said source of current and to a respective one of the remaining windings of said plurality and to a respective one of said multivibrator means and each operatively responsive to the gating voltage of the multivibrator means to which connected, and coincidence tube means connected to said parallel circuit and to the last multivibrator means in said sequence operative responsively to the resonant frequency output of said parallel circuit to produce an output signal only for the duration of the gating voltage produced by said last multivibrator means. 5. A permutation coding circuit comprising a magnetic core inductance having at least three discrete magnetically linked windings, a capacitance connected to form a parallel circuit with the first of said windings, means for applying incoming signals to said parallel circuit, a first multivibrator means connected to said parallel circuit for producing a first gating voltage of predetermined duration in response only to the resonant frequency output of said parallel circuit, a source of current, direct current control means connected in serieswith said source of current and the second of said windings and to said first multivibrator means operatively responsive to said first gating voltage, a second multivibrator means connected to said parallel circuit and to said first multivibrator means for producing a second gating voltage of predetermined duration in response to the resonant frequency output of said parallel circuit only for the duration of said first gating voltage, direct current control means connected in series with said source of current and the third of said windings and to said second multivibrator means operatively responsive to said second gating voltage, and coincidence tube means connected to said parallel circuit and to said second multivibrator means operative responsively to the resonant frequency output of said parallel circuit to produce an output signal only for the duration of said second gating voltage.

6. A permutation coding circuit comprising a magnetic core inductance having at least three discrete magnetically linked'windings, a capacitance connected to form a parallel circuit with the first of said windings, means for applying incoming signals to said parallel circuit, a first vacuum tube keying means connected to said parallel circuit for producing a keying signal in response only to the resonant frequency output'of said parallel circuit, a first multivibrator connected to said first keying means for producing a first gating voltage of predetermined duration in response only to the output of said keying means, a source of current, direct current control means connected in series with said source of current and the second of said windings and to said first multivibrator operatively responsive to said first gating voltage, a second vacuum tube keying means connected to said parallel circuit and to said first multivibrator for producing a keying signal only in response to the coincidental occurrence of said first gating voltage and the resonant frequency output of said parallel circuit, a second multivibrator connected to said second keying means for producing a second gating voltage of predetermined duration in response only to the output of said second keying means, direct current control means connected in series with said source of current and the third of said windings and to said second multivibrator operatively responsive to said second gating voltage, and coincidence tube means connected to said parallel circuit and to said second multivibrator for producing an output signal only in response tothe coincidental occurrence of said second gating voltage and the resonant frequency output of said parallel circuit.

7. A permutation coding circuit comprising a magnetic core inductive winding, a capacitance connected to form a parallel circuit with said winding, means for applying incoming signals to said parallel circuit, a sequence of serially connected multivibrator means for producing gating voltages each connected to said parallel circuit and each, except the first, operatively responsive 10 to the resonant frequency output of said parallel circuit only for the duration of the gating voltage produced by the immediately preceding multivibrator means in said sequence, a source of current, a plurality of direct current controlling means connected in parallel one with the other and eachin series between said source of current and said inductive winding, each of said direct current controlling means also being connected to a respective one of said multivibrator means and being operatively responsive to the gating voltage of the multivibrator means to which connected, and coincidence tube means connected to said parallel circuit and to the last multivibrator means in said sequence operative responsively to the resonant frequency output of said parallel circuit to produce an output signal only for the duration of the gating voltage produced by said last multivibrator means.

CONRAD H. HOEPPNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,547,226 Martin July 28, 1925 2,330,216 Hoover et a1 Sept. 28, 1943 2,394,786 Korneke Feb. 12, 1946 FOREIGN PATENTS Number Country Date 172,321 Great Britain Nov. 2, 1922 393,327 Great Britain June 8, 1933 444,316 Great Britain Mar. 18, 1936 

